The present invention relates to improved methods and apparatus for lathe cutting lenses, especially contact lenses, from a blank or button.
A conventional method of manufacturing lenses, especially contact lenses, involves lathing the lens from a cylindrical blank of polymerized lens material (such cylindrical blanks commonly referred to as a xe2x80x9cbuttonxe2x80x9d). The buttons may be cut initially from rod stock or sheets, or individually cast in cups using a curable liquid monomeric composition.
While it is possible in some cases to insert the button directly into the lathe collet, it is more typical to first attach the button to a separate metal pin or xe2x80x9cblockxe2x80x9d, the opposite end of the block being configured for removable insertion into the collet of the lathe. The button is typically adhered to the block with an adhesive or special type of wax called xe2x80x9cpitchxe2x80x9d (with the block thus commonly referred to as a xe2x80x9cpitch blockxe2x80x9d in the art). While the block and button are turned, the desired concave (or xe2x80x9cbasexe2x80x9d) curve is lathed into the exposed end of the button opposite the adhered end. Subsequently, this semi-finished button is deblocked from this first base curve metal block, for example, by removing the pitch adhering the button to the metal block.
Then, this partially-finished button is adhered to a second metal block such that the lathe cut base curve of the button is adhered to the second metal block, again typically with pitch, while attempting to maintain proper alignment vis-a-vis the second metal block and the cut base curve. This front curve metal block is mounted to a lathe collet for lathing the convex (or xe2x80x9cfrontxe2x80x9d) curve from the button. Subsequently, the lens must be deblocked from the front curve metal block.
These operations may also involve intermediate lathing operations, for example, cutting a desired precision thickness or cutting an edge chamfer in the button, prior to lathing the front curve. Also, typically these operations will involve lens edging and polishing operations on the lathe cut surfaces.
The multiple mounting and removal operations of the button to and from the blocks during the overall lathing process consume a significant amount of time and are prone to error, especially in maintaining the necessary axial alignment between the base curve block and the front curve block. Also, deblocking of the button or lens from the metal blocks to remove pitch requires the undesirable use of solvents or liquid suspension media as well as adds to the manufacturing cycle time.
This invention provides an improved method of lathing a lens, especially a contact lens, from a cylindrical blank. According to a first embodiment, the method comprises: attaching the cylindrical blank of lens material to a block of machineable plastic material; mounting the block in a lathe collet and lathe cutting a desired first lens surface in the cylindrical blank; attaching the machined first lens surface of the blank to a second block while the blank remains adhered to the block of machinable plastic material; mounting the second block in a lathe collet, and lathe cutting to remove the block of machineable plastic material; and lathe cutting a desired second lens surface, opposite the first lens surface, in the blank.
According to various preferred embodiments, both the first block of machineable plastic material and the second block are adhered to the lens blank with an adhesive curable by ultraviolet radiation.
According to various other preferred embodiments, the second block is composed of a head section and a body section, the head section comprising a convex upper surface for adhering to the concave base curve of the blank, and the body section comprising an elongated cylindrical body. A lower portion of the head section is releasably securable in an upper portion of the body section. The body section can be separated from the head section with the lens being retained on the head section, with the body section being recycled for additional cycles. Subsequently, the lens can be separated from the head section of this second block, for example, by immersion in a heated aqueous bath.
The invention also provides a method of preparing a cylindrical blank of lens material for lathe cutting a lens therefrom comprising attaching to the lens blank a block of plastic material with an adhesive curable by ultraviolet radiation, said block being transparent to ultraviolet radiation, and transmitting ultraviolet radiation through the block to cure the adhesive; and, following lathe cutting a desired first lens surface in the blank, attaching to the cut first lens surface of the blank a second block of plastic material with an adhesive curable by ultraviolet radiation, said second block being transparent to ultraviolet radiation, and transmitting ultraviolet radiation through this second block to cure the adhesive.
The invention permits precise axial alignment of the second block with respect to the lens blank having a first curve lathe cut therein. Additionally, the invention avoids deblocking operations that require a solvent and are more time intensive.